Radioimmunoassay is generally defined as those techniques which employ the principle of isotopic dilution in the presence of specific antibodies. This principle finds many uses in the laboratory, for example, in detecting the presence of the hepatitis associated antigen (HAA) in serum. In this regard, the "sandwich principle" is gaining in popularity.
The sandwich principle in HAA detection denotes the sandwiching of antigens between antibodies. More specifically, when a serum containing HAA is added to a test tube whose walls have previously been coated with antibodies, the HAA binds to the antibodies on the walls of the tube. Then, after rinsing, radioactive antibodies added to the tube link with the previously bound antigen, creating the "sandwich." Radioimmunoassay relates to the technique for detecting and determining the level of radioactivity remaining in the so-treated test tube. Without the presence of HAA, the radioactive antibodies will be rinsed from the tube, and hence relatively no radiation will be detected. However, if HAA was present, the radioactive antibodies will remain linked in the sandwich on the walls of the test tube, and a relatively high level of radiation will be detected.
In the past, samples of the type described above have been tested for radioactivity in several ways. One procedure which is still popular is the manual procedure, in which the test tubes containing the samples are tested one by one. The tubes are sequentially manually inserted into a radiation detector, the level of radiation is read and recorded, and the tubes are removed. With this procedure, it is of course necessary that a technician always be present.
Modern technology has, to some extent, improved the manual technique noted above. There are automatic sample changers on the market today which accept a plurality of samples for testing, and which automaticaly transport and test the samples, and record the level of radiation so detected. However, each of these known automatic sample changers suffers from one or more of several drawbacks. Many are quite large, complex, and accordingly expensive. Others are limited to accepting only a small number of samples. And still others, capable of receiving many samples, cannot accept the standard size test tube. Furthermore, many of the known automatic sample changers can be dangerous if misused by the attendant technician.
It is the purpose of the present invention to provide an automatic sample changer which eliminates the drawbacks of the prior art which have been noted above.